Radio Frequency Identification (RFID) systems are used for identification and/or tracking of equipment, inventory, or living things. RFID systems are radio communication systems that communicate between a radio transceiver, called an Interrogator, and a number of inexpensive devices called Tags. In RFID systems, the Interrogator communicates to the Tags using modulated radio signals, and the Tags respond with modulated radio signals. After transmitting a message to the Tag (called the Downlink), the Interrogator then transmits a Continuous-Wave (CW) radio signal to the Tag. The Tag modulates the CW signal using modulated backscattering where the antenna is electrically switched, by the modulating signal, from being an absorber of RF radiation to being a reflector of RF radiation. This modulated backscatter allows communications from the Tag back to the Interrogator (called the Uplink). Conventional MBS systems are designed a) to identify an object passing into range of the Interrogator, and b) to store data onto the Tag and then retrieve that data from the Tag at a later time in order to manage inventory or perform another useful application.
Let us concentrate our attention to applications in a campus environment or inside a building, and first consider the use of RFID technology for "Security" applications. RFID is today used in the security industry to facilitate building access; for example, the use of an RFID Tag to automatically authorize entrance to a building, or to record that an individual passed by a particular location. This operation is called the Interrogation Mode--a mode of operation where the Interrogator transmits a signal to all Tags in the reading field, requesting those Tags to respond with data which identifies this Tag. The Tag then transmits this information back to the Interrogator using MBS.
In addition, "Location" applications exist within a building or campus. (For the remainder of this disclosure, we will use the term "building" or "in-building" to mean either within a building or within a campus environment which could include a building.) For example, it would be beneficial to know the location of a specific Tag within the building. This could be of benefit in high-security locations. Other applications of this capability include the ability of the in-building telephone system to route telephone calls to a phone close to where an individual is presently located. There have been prototype systems, using infrared transmitters, to address this application; however, there are no commercial products, and infrared technology suffers from lack of range and an inability to pass through objects. Thus, if the infrared transmitter is placed inside a person's shirt pocket, the communications path is blocked. Thus, today, there are no cost-effective solutions to the location problem.
In addition, low speed data "Communications" applications also exist. An example of a current system to provide low-speed data communications is Paging. Some Paging systems suffer from poor in-building wireless coverage, and some Paging systems require paying usage charges to a service provider on a per-transaction basis. Another alternative is to deploy a wireless data LAN in the building; however these products are still relatively expensive. In addition, none of the current low speed data communications alternatives address the Security or Location issues discussed above. Our goal is a system that will simultaneously address the Security, Location, and low-speed data Communications applications.
In this disclosure, we disclose how a radio frequency identification system, utilizing modulated backscatter, can be used to integrate the functions of Security, Location, and low speed data Communications in a single system with a single infrastructure. This invention can provide improved security as well as cost-effective in-building or campus area location and communications services.